Citation: To use information from this web resource in your work, please cite this as follows:
Cranfield University 2018. The Soils Guide. Available: www.landis.org.uk. Cranfield University, UK. Last accessed 18/02/2018

Covers 50 km2 in England and Wales

Soilscapes Classification

0643b Poundgate

Detailed Description

This is the principal soil association in Ashdown Forest, a scenic tract of heathland and woodland with a little farmland situated at the heart of the High Weald west of Crowborough in East Sussex. It is characterized by very acid podzolized soils formed and still largely under open heath. Associated with these are other acid soils on wet heathland, bogs and under old woodland. The association also occurs in wooded country south of Tunbridge Wells.

Ashdown Forest lies on a broad ridge of high ground at 170-240 m O.D., deeply dissected to the north by steep-sided valleys draining to the Medway, and more gently dissected to the south by tributaries of the Sussex Ouse. The ridge is formed by siltstones and very fine-grained sandstones of the Ashdown Beds which, with locally derived Head and colluvium in the valleys, give dominantly silty or loamy soils. The soils have been described and mapped by Abbas (1979).

On the level or gently sloping land of the ridge summit, the dominant soil is the Poundgate series, stagnogley-podzols, consisting of very fine sandy or silty upper horizons, differentiated by podzolization from slowly permeable gleyed silty horizons below containing abundant sandstone fragments, which rest in turn on compact interbedded siltstone and sandstone. Most profiles are moderately deep, but shallow Poundgate soils and some loamy stagnopodzols with diffuse ironpan occur locally where the underlying rock is harder. Shallow Curtisden soils, stagnogleyic argillic brown earths, often sandier than usual elsewhere, are interspersed with coarse loamy Rivington soils or sandy podzolic Shirrell Heath soils both of which overlie sandstone. Occasional fine sandy Shedfield soils, flank the ridge summits and give way downslope to the Cranbrook series, deep silty typical stagnogley soils. Ashdown series, cambic stagnohumic gley soils with a humose surface horizon over gleyed loamy horizons, is characteristic of wet heathland on lower slopes and around the numerous springs and flushes. Moderately deep or deep silty Curtisden soils are common on wooded slopes along the northern margin of the Forest, but are also interspersed amongst Poundgate and Cranbrook soils elsewhere. South of Tunbridge Wells the association is on lower land between 100 and 130 m O.D. over Ashdown Beds. Here the land is mainly under coniferous plantations with reclaimed areas of farmland on which, despite cultivation, traces of former heathland soils are still found. At Rushlye Down, dry podzols of the Shirrell Heath series are more common than Poundgate soils.

Soil Water Regime

The annual rainfall on Ashdown Forest is over 900 mm, relatively high for South East England, often giving rise to wet soil conditions under semi-natural vegetation. The slowly permeable compact subsoils of Poundgate series cause seasonal waterlogging (Wetness Class III) and in Cranbrook soils lead to long periods of waterlogging in winter (Wetness Class IV). Curtisden soils are less frequently waterlogged (Wetness Class III), whereas Ashdown soils are more or less permanently waterlogged (Wetness Class VI). The permeable upper horizons of the soils usually absorb excess winter rain but run-off occurs after prolonged periods of heavy rainfall and erosion of bare soil along paths and tracks on slopes is common. Drainage measures reduce the duration of waterlogging in most situations, but silting of pipes and shifting of springs makes long-term control difficult to achieve. The large or very large profile available water of these mainly silty soils means that grass or cereal crops, where grown, are unlikely to suffer drought in most years.

Cropping and Land Use

Originally part of the extensive Wealden Forest, some 5700 ha of land was set aside at Asshes Doune (Ashdown) in 1268 as a Royal Hunting Forest. During the 16th and 17th centuries the forest supplied fuel to the forges of the iron industry and timber for ships and houses. Cropping far exceeded regeneration, so with substantial local enclosure by 1879 there was "hardly a bush to be seen above the level of the heather and bracken". Commoners' rights to cut litter and to graze stock have been confirmed in several Acts of Parliament, culminating in the Ashdown Forest Act (1974) which gives management of the 2600 ha of remaining commonland to a Board of Conservators. Their duties include management of the Forest as an "amenity and place of resort", and to conserve it as a "quiet and natural area of outstanding beauty". Thus recreational activities of walking, horse-riding and picnicking are encouraged at the same time as preserving the wildlife and preventing increasing encroachment of heathland by trees and scrub. The commoners, now many fewer than in the past, formerly maintained the heath by the grazing, burning and cutting of bracken and heather for bedding stock.

Old woodland in Ashdown Forest, including both oak and beech is associated with Curtisden soils around Hindleap Warren in the northern part, but the heathland and bog communities are of greater interest to naturalists. Dry heathland on Poundgate and shallow Curtisden soils is a mosaic of plant communities largely determined by the past incidence of fires. The four main communities are dominated respectively by ling (Calluna vulgaris), gorse (Ulex europaeus), bracken (Pteridium aquilinum) and an association of dwarf furze (Ulex minor) and purple moor-grass (Molinia caerulea). On the wet heathland on Ashdown and Cranbrook soils, ling and cross-leaved heath (Erica tetralix) are associated with deer-grass (Trichophorum cespitosum) and bog moss (Sphagnum spp.). A number of other species occurring only rarely elsewhere in the south-east include sundews (Drosera spp.), marsh clubmoss (Lycopodiella inundata) and the white beak-sedge (Rhynchospora alba). Bog moss dominates the mires in valley bottoms. Here, as well as the main wet heathland species, cotton-grass (Eriophorum angustifolium), bog asphodel (Narthecium ossifragum) and sharp-flowered rush (Juncus acutiflorus) are also present. Today, Scots pine and birch are invading the heathland and willows the mires; following heathland fires, bracken tends to take over from ling, and purple moor-grass is spreading in wet heathland.

Forestry is confined to private estates, and consists mainly of coniferous plantations on the poorest, shallowest soils. Subsurface pans in Poundgate soils or bed¬rock at shallow depth in Curtisden soils require tine ploughing before establishment to give better rooting for young trees, to aid surface drainage and to suppress heathers on heathland. Scots pine, Corsican pine and Douglas fir are the most suitable species for these acid soils low in nutrients. Deep Curtisden soils are more fertile, so the range of suitable species includes larch, Norway spruce, western hemlock and the hardwoods beech and oak. On Cranbrook soils yields are limited by shallow rooting caused by waterlogging. Alder and poplar are the best suited tree species for the wetter Ashdown soils and boggy sites.